I, honestly, have had no trouble with the extension at all... but I also understand some of the intricacies for less advanced users can be problematic. The few people that emailed me were asking me how I created a few of my forms and I think their real issue was grasping the fieldset and then editing the groups where you add lines and elements inside lines, etc.
That was the only area that I thought the documentation was lacking from their point of view. It appears that there could be some more detail in both creating the form elements correctly (because you can actually create elements at the fieldset level but it doesn't perform correctly, as opposed at the group level with lines and sets) and the styling of form elements.
For me, like I said, it all is great but I probably get a handle on these things quicker than many other typical users.
Great product, though. Keep up the good work.